Lamps, such as of Par 36 type, provide signaling and warning functions for vehicles, such as buses, trucks, locomotives, or planes. These lamps have housings designed to be received in fixtures or brackets mounted in a hole drilled in an external surface of a vehicle's body. Wires from the lamp may then be connected to the vehicle's electronics to supply power and function control. Such inset mounting of a lamp may be acceptable where a vehicle's body can accommodate a hole for receiving the lamp and its mounting fixture; however, often this is not the case and the lamp must be on-surface mounted instead (or if otherwise considered more desirable than inset mounting). This necessitates use of an entirely different lamp model having a housing designed for an on-surface mounting fixture. As a result, lamps having the same optical design require two different housing configurations, one for each different type of mounting modes, e.g., inset surface mounted or on-surface mounted, as desired for the particular vehicle applications. It would thus be desirable to provide a lamp having a housing that can be mounted to a vehicle regardless of the mounting mode needed, thus avoiding manufacturing lamps of the same optical design having different housings to accommodate different mounting modes.